Chromopeptides were prepared by proteolytic digestion of phytochrome (far-red absorbing form, Pfr) and of phycocyanin. The phycocyanobilin peptide, the chromophore of which is Z,Z,Z-configurated, was modified to the Z,ZE isomeric chromophore. It has been demonstrated earlier that the Pfr chromopeptide and the Z,Z,E-configurated phycocyanin chromopeptide behave similarly with regard to spectral and chromatographic properties and reactivity. We present evidence here, obtained by high-resolution 'H NMR spectroscopy, that both the modified phycocyanobilin chromophore and the phytochrome chromophore obtained directly from Pfr are 15E-configurated.Plant development is influenced by light in many ways. An important photoreceptor of higher plants is the chromoprotein phytochrome (1-3), which can mediate light-dependent irreversible differentiation (e.g., seed germination, flowering, and stem and leaf growth) and reversible modulations (e.g., leaflet or chloroplast movement, root tip adhesion, and transmembrane potentials).A characteristic property of phytochrome in vivo (in the plant cell) and in vitro is its photoreversibility. The physiologically inactive (red-absorbing) Pr form (Ama. = 660 nm) is transformed by red light to the physiologically active Pfr form (Amak = 730 nm), which in turn is reconverted by far-red light to the Pr form. nm Pr = Pfr 730 nmThe chemical structure of the Pr chromophore (structure la), including its linkage to the protein, was elucidated by combination of oxidative degradation and UV/visible spectroscopy (4-6), by comparison of the cleaved chromophore with the product obtained by total synthesis (7,8), and by high-resolution NMR spectroscopy of a chromopeptide (9). It is closely related to the structure of the phycocyanin chromophore

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A tale of two modes: An end‐on copper superoxo complex was identified in a combined experimental and theoretical study. Theory clearly discloses the presence of an end‐on complex (see picture, O red, Cu pink, N green) with a minute isotopic resonance Raman splitting below experimental resolution. The results cast doubts on the uncritical use of 16O,18O isotopic‐labeling Raman experiments to discriminate end‐on from side‐on bonding modes in M(O2) complexes.

The competition between conformational dynamics and electron transfer within a series of phenothiazine-(phenyl) n -pyrene (n ) 0, 1) electron donor-acceptor dyads of potential use in organic light emitting diodes was examined using femtosecond transient absorption spectroscopy. The molecular structures of these dyads permit only torsional motions around the single bonds joining each aromatic subunit. The redox properties of these molecules are nearly independent of the phenyl bridging group, whereas spectroelectrochemistry shows that the UV/vis absorption spectra of the oxidized and reduced species vary with the bridge. Each molecule exhibits dual fluorescence emission which provides evidence for conformational heterogeneity. Emission from a locally excited state originates from a minority conformation, in which electron transfer is negligible, whereas emission because of ion pair recombination results from the majority conformation which undergoes electron transfer. The electron-transfer reactions proceed with time constants <25 ps except in the dyad with the longest donor-acceptor distance in nonpolar solution, where the free energy of the charge separation reaction is positive. If electron transfer is sufficiently fast, conformational relaxation within the ion pair state product occurs on a 100-400 ps time scale, whereas if electron transfer is slow, conformation relaxation with the locally excited state centered on phenothiazine occurs. In two of the dyads in nonpolar solvents, wherein the free energy for charge separation is estimated to be very small, strong mixing between the ion pair state and the locally excited state of phenothiazine is found. The results show that competitive conformational relaxations can have a strong influence on the charge separation dynamics of donor-bridge-acceptor molecules with single bond linkages. In turn, these conformational dynamics will undoubtedly have an important influence on the photophysics of these molecules in the solid-state environment characteristic of light-emitting diodes. † Part of the special issue "Edward Schlag Festschrift".

At low temperatures, the mononuclear copper(I) complex of the tetradentate tripodal aliphatic amine Me(6)tren (Me(6)tren = tris(2-dimethylaminoethyl)amine) [Cu(I)(Me(6)tren)(RCN)](+) first reversibly binds dioxygen to form a 1:1 Cu-O(2) species which further reacts reversibly with a second [Cu(I)(Me(6)tren)(RCN)](+) ion to form the dinuclear 2:1 Cu(2)O(2) adduct. The reaction can be observed using low temperature stopped-flow techniques. The copper superoxo complex as well as the peroxo complex were characterized by resonance Raman spectroscopy. The spectral characteristics and full kinetic and thermodynamic results for the reaction of [Cu(I)(Me(6)tren)(RCN)](+) with dioxygen are reported.

Reduction of aqueous silver nitrate by hydrazine dihydrochloride in weakly alkaline solution results in a polydisperse colloid that is stable for many months without addition of any stabilizing compounds. The average size of the predominantly spherical particles depends on the initial concentration of silver ions, ranging between 40 and 70 nm in diameter. The colloidal solutions exhibit a characteristic absorption in the blue region of the visible spectrum and are not turbid below a formal silver concentration of 4.5 × 10 -4 M. With colloids prepared from 1.5 × 10 -4 M silver(I), the SERS spectra of dyes such as nile blue A could be recorded from a solution with concentrations as low as 10 -10 M, whereas no SERS signal was observed for dye concentrations higher than 10 -4 M. The maximum signal intensity was obtained at a concentration of about 10 -7 M. With colloids prepared from g3 × 10 -4 M silver(I), no SERS signal was obtained from highly diluted solutions, but the concentration limit for the maximum signal intensity of around 10 -7 M became even sharper. The thus prepared silver colloids can therefore be recommended for qualitative detection of certain organic compounds in the parts per billion range as well as for a semiquantitative determination in the parts per million range.

IR and Raman (λex = 785 and 1064 nm) spectra of Fe(phen)2(NCS)2 were recorded at T = 298 and 100 K, and the observed vibrations were assigned by comparison with the results obtained by DFT/BP86 calculations. The latter resulted, in accordance with crystal data, in an equilibrium geometry with C 2 symmetry for the low-spin state. In the high-spin state, two closely lying extrema were found on the BP86 energy hypersurface:  a saddle point (C 2 symmetry, one imaginary vibrational frequency) and, ca. 9.6 kJ/mol lower in energy, a minimum with C 1 symmetry. The differences in the geometrical parameters of the low-spin and high-spin states are in good agreement with the changes observed experimentally by X-ray crystallography. The calculated wavenumbers of the (NCS) vibration differed from the experimentally determined ones by more than 50 cm-1. Since it could be shown that anharmonicity is not the only cause for this discrepancy, two pyridins at optimized distances were included to model the interaction in the crystalline state. We find a correct wavenumber shift of this solid-state model versus the isolated molecule, corroborating the prominent role of intermolecular interactions, which are considered to be responsible for the sharp transition from the low-spin to the high-spin state. The partition function was calculated for both spin states by considering all calculated vibrational wavenumbers. The vibration-related entropy change connected with the low- to high-spin transition is determined via well-known thermodynamic relations. For the title compound, we found ΔS vib ≈ 19.5 J/(mol K), or approximately 40% of the experimentally determined total entropy change of 49 J/(mol K).

Steady-state absorption and emission, circular dichroism (CD), and time-of-flight secondary-ion-mass-spectroscopic (TOF−SIMS) measurements were performed to study the complexation of tetracycline (TC) and anhydrotetracycline (AHTC) with Mg2+ and Ca2+ ions, respectively, in aqueous solutions at pH 8.02. The results obtained suggest that Ca2+ forms a 1:2 ligand:metal complex with TC via chelation through O10−O11 and O12−O1 and induces thereby the extended conformation A of TC, which is stabilized through hydrogen bonding between the deprotonated dimethylamino nitrogen, N4, and OH12a. pH titrations provide evidence that N4 deprotonates in the presence of a 164-fold molar excess of Ca2+ at approximately pH ⩾ 7.7 (c TC = 2.1 × 10-5 M). In contrast to Ca2+, Mg2+ binds to N4−O3 and thereby stabilizes the twisted conformation B of TC. TOF−SIMS measurements indicate that a 1:2 ligand:metal complex is formed in addition to the 1:1 complex. The Mg2+-induced increase in the fluorescence intensity and the observed changes in the absorption spectra provide evidence that the other Mg2+ ion binds to the BCD ring system through the deprotonated O11. In contrast to TC, which adopts the twisted conformation B in aqueous solution at pH 8.02, AHTC exhibits the extended conformation A due to slightly lower deprotonation constants. In the presence of Mg2+, however, the conformational equilibrium is shifted toward the twisted conformation B due to binding of Mg2+ to N4. TOF−SIMS measurements suggest that a 2:2 ligand:metal complex is formed. AHTC remains in conformation A upon addition of Ca2+; complexation through O10 can be excluded on the basis of absorption spectroscopic data.